Various heat generating devices of the type having a heat generating material sealed in an air-permeable flat bag which are used to warm a body part by the heat generated by the heat generating material are known. For example, Patent Document 1 assigned to the common assignee of the present invention proposes a portable body warmer including a heat generating main body and a flap. The heat generating main body includes an outside layer, an inside layer, and a heat generating element interposed between the outside and inside layers. The flap extends outward from an upper edge of the heat generating main body and is designed to be attached to panties (undergarment) when the body warmer is used. Both the heat generating main body and the flap have an adhesive applied thereto so that the heat generating main body is attached to the outer side of panties via the adhesive, while the flap is folded over the waist opening of the panties and attached to the inner side of the panties. Therefore, the position where the body warmer is attachable is limited to near the waist opening of the wearer's panties. Since the heat from the body warmer is transmitted to the body indirectly via the panties, the heat transfer efficiency can vary depending on the textile material of the undergarment.
Apart from the portable body warmer described above, a thermal body pad for relieving menstrual pain is proposed in Patent Document 2. The thermal body pad includes a plurality of heat cells having an exothermic material sealed in between two layers and has a first side with oxygen permeability and a second side which is to be placed directly against a user's body. The oxygen permeable first side is provided with a self-adhesive attachment means for releasably fixing the body pad. The attachment means is provided over the whole area of the first side, via which the body pad is attached to an inside portion of a user's undergarment. Since the self-sensitive attachment means is provided on the whole area of the first side, if the body pad is attached to user's panties with its upper portion sticking from the waist opening of the panties, the adhesive attachment means of the sticking portion would adhere to other user's clothing. Even when the body pad is attached to a right position of user's panties, attachment and/or removal of the body pad are liable to cause pubic hair to adhere to the self-adhesive attachment means. The user's fingers are also apt to be caught by the self-adhesive attachment means in attaching and/or removing the body pad. That is, the body pad lacks handling convenience. Although the body pad applied directly to a user's body on its second side achieves direct heat transfer, a number of the heat cells provides a lumpy feel to the body to cause discomfort.
Besides the body pad of Patent Document 2, known heat generating devices having an adhesive attachment means include a heat generating pack having a heat generating composition sealed in a flat pack having an air permeable adhesive side and a non-adhesive side (see Patent Document 3). The heat generating pack is designed to be attached to an inner portion of a user's undergarment on its air-permeable adhesive side so that the air-permeable adhesive side faces opposite to the body thereby maintaining stable air permeation and that the non-adhesive side is brought into contact with a user's body thereby directly warming the body. The adhesive is uniformly and discretely applied to the air-permeable side by printing or coating. Therefore, the heat generating pack has the same disadvantages of the body pad of Patent Document 2. Furthermore, since the air-permeable adhesive side, through which air should pass, faces an undergarment, some undergarment fabrics can interfere with sufficient air supply. Reduction of the area where the adhesive is applied in an attempt to secure air passage can also result in a failure to provide sufficient adhesive strength.    Patent Document 1: JP 11-155895A    Patent Document 2: WO98/29063A1    Patent Document 3: JP 2001-198150A